The present invention relates generally to golf balls exhibiting high potential spin rate characteristics. More particularly, the invention relates to high spinning golf balls having a relatively soft, high resilience, solid polybutadiene core and a soft outer cover. Preferably, the balls are of two-piece construction comprising a large core and a thin cover.
Until relatively recently, many highly skilled, low handicap golfers had utilized wound golf balls for competitive play. These balls have a wound core (i.e., a liquid or solid center and elastic windings) and a balata or balata-like cover.
Balata covered wound golf balls are known for their soft feel and high spin rate potential. However, balata covered balls suffer from the drawback of low durability. Among other things, even in normal use, the balata covering can become cut and scuffed, making the ball unsuitable for further play. Additionally, the internal elastic windings are susceptible to breakage upon ball striking, and/or the center of the ball can be knocked off center or xe2x80x9cout of roundxe2x80x9d. Furthermore, the coefficient of restitution of wound balls is reduced at low temperatures.
The problems associated with balata covered balls have resulted in the widespread use of durable ionomeric resins as golf ball covers. However, balls made with ionomer resin covers typically have higher PGA(copyright) compression ratings. Those familiar with golf ball technology and manufacture will recognize that golf balls with higher PGA(copyright) compression ratings are considered to be harder than conventional balata covered balls.
Consequently, it would be useful to develop a golf ball having a durable, yet comparatively soft, cover which has the sound and feel of a balata covered wound ball. It would also be useful to develop a solid core golf ball having the overall desired spin and flight characteristics exhibited by balata covered wound balls.
Taken as a whole, the solid core balls of the present invention exhibit the high spin (mid-iron through wedge), flight characteristics (i.e., launch angle, trajectory, etc.) and feel produced by balata covered wound golf balls. The balls of the invention also exhibit enhanced durability with equal or superior distance.
The present invention is accomplished, in part, by combining a soft, durable cover with a relatively soft, solid core. The core is constructed using high molecular weight polybutadiene or other rubbers exhibiting enhanced coefficient of restitution (C.O.R.). The golf balls of the invention have a core compression and an overall ball PGA(copyright) compression of 90 or less, preferably less than 80, and most preferably less than 75. The hardness of the cover is soft enough so that the PGA(copyright) compression of the overall ball is substantially the same or lower than that of the core.
Moreover, the properties of the core and/or cover of the balls of the invention can be adjusted to obtain the particular spin rates desired. For example, larger or heavier cores can be utilized for even greater spin rates, (although lower C.O.R. may result), softer covers can be utilized for higher spin rates, etc. Preferably, the golf balls of the present invention utilize relatively large, soft cores and thin, soft covers. The cores and/or balls of the invention can be optionally irradiated to additionally improve such properties as C.O.R., scuff, and melt resistance.
In addition, the particular dimple pattern of the balls can be selected to further optimize the desired spin rates. Similarly, the flight/trajectory of the ball can be adjusted depending upon the dimple pattern selected and the core and cover materials utilized in construction.
Prior to the present invention, high spin, two-piece golf balls consisted generally of hard cores having covers varying in hardness/softness. The hard cores were necessary to achieve the desired resiliency, i.e., C.O.R., needed for enhanced distance, etc. Additionally, hard cores were utilized to produce higher spin rates. This is because at impact, the hard core compresses the cover of the ball against the clubface to a much greater degree than a soft core. This compression results in more xe2x80x9cgrabxe2x80x9d of the ball on the clubface and subsequent higher spin rate. In effect the cover is squeezed between the relatively incompressible core and clubhead. When a softer core is used, the cover is under much less compressive stress than when a harder core is used and therefore does not contact the clubface as intimately. This results in lower spin rates.
However, while the hard core, two-piece balls exhibited enhanced spin rates, this was essentially for all clubs. Additionally, the hard core, two-piece balls produced generally a poor, or hard, responsive feel to the golfer.
The resulting balls of the present invention utilize a soft, high resilience core and a relatively thin, soft cover. Preferably, the balls of the invention comprise two-piece golf balls. The balls produce high spin rates, equal to or greater than balata covered wound golf balls with the same or better distance. The balls also produce improved feel over traditional two-piece golf balls.
Additionally, machine and limited player testing also indicates that the flight/trajectory of the balls of the invention approaches the xe2x80x9crisingxe2x80x9d trajectory exhibited by the balata covered wound golf balls. The xe2x80x9crisingxe2x80x9d, as opposed to a xe2x80x9cboringxe2x80x9d or xe2x80x9cpenetratingxe2x80x9d trajectory, is preferred by players who find it difficult to attack tight pin positions or be those who find it difficult to keep the ball in narrow fairways off the tee.
With respect to several of the enhanced properties of the invention, two of the principal properties involved in the performance of golf balls are resilience and hardness. Resilience is determined by the coefficient of restitution (referred to as xe2x80x9cC.O.R.xe2x80x9d), also expressed as the constant xe2x80x9cexe2x80x9d, which is the ratio of the relative velocity of two elastic spheres after direct impact to that before impact, or more generally, the ratio of the outgoing velocity to incoming velocity of a rebounding ball. As a result, the coefficient of restitution (i.e. xe2x80x9cexe2x80x9d) can vary from zero to one, with one being equivalent to an elastic collision and zero being equivalent to an inelastic collision.
Hardness/softness of a ball is determined as the deformation (i.e. compression) of the ball under various load conditions applied across the ball""s diameter. The lower the deformation, the harder the material.
Resilience (C.O.R.), along with additional factors such as clubhead speed, angle of trajectory, and ball configuration (i.e. dimple pattern), generally determine the distance a ball will travel when hit. Since clubhead speed and the angle of trajectory are not factors easily controllable, particularly by golf ball manufacturers, the factors usually of concern among manufacturers are the coefficient of restitution (C.O.R.) and the surface configuration of the ball.
In this regard, the coefficient of restitution of a golf ball is generally measured by propelling a ball at a given speed against a hard surface and electronically measuring the ball""s incoming and outgoing velocity. The coefficient of restitution is believed to be carefully controlled in all commercial golf balls in order for the ball to be within the specifications regulated by the United States Golfers Association (xe2x80x9cU.S.G.A.xe2x80x9d).
Along this line, the U.S.G.A. standards indicate that a xe2x80x9cregulationxe2x80x9d ball cannot have an initial velocity (i.e. the speed off the club) exceeding 255 feet per second (250 feet per second with a 2% tolerance). Since the coefficient of restitution of a ball is related to the ball""s initial velocity (i.e. as the C.O.R. of a ball is increased, the ball""s initial velocity will also increase), it is highly desirable to produce a ball having a sufficiently high coefficient of restitution to closely approach the U.S.G.A. limit on initial velocity, while having an ample degree of hardness (i.e. impact resistance) to produce enhanced durability.
The coefficient of restitution (C.O.R.) in solid core balls is a function of the composition of the molded core, the intermediate layers (if any) and of the cover. In balls containing a wound core (i.e. balls comprising a liquid or solid center, elastic windings, and a cover), the coefficient of restitution is a function of not only the composition of the center and cover, but also the composition and tension of the elastomeric windings.
Polybutadiene rubber has been utilized for years in forming molded golf ball cores. Prior artisans have investigated utilizing various grades of polybutadiene in core compositions. For example, such attempts are described in U.S. Pat. Nos. 5,385,440; 4,931,376; 4,683,257; 4,929,678; 4,955,613; 4,974,852; 4,984,803; 5,082,285; and 5,585,440; and in Japanese Patent References JP 58225138 and JP 7268132, all of which are hereby incorporated by reference. Although some of the core compositions described in these disclosures are somewhat satisfactory, a need remains for an improved composition for forming golf ball cores.
Accordingly, it is an object of the present invention to provide an improved polybutadiene composition which, when utilized to formulate golf ball cores, produces golf balls exhibiting enhanced C.O.R. without increasing hardness. An additional object of the invention is to produce a durable, soft golf ball core from a polybutadiene composition having a high Mooney viscosity and/or a high molecular weight and low dispersity.
Additionally, it is another object of the present invention to provide an improved core composition which, when utilized to formulate golf ball cores, produces golf balls exhibiting enhanced C.O.R., relatively soft compression and improved processing.
A further object of the invention is to combine the improved core composition with a durable, yet relatively soft, cover material. Various cover compositions have been developed in order to optimize, along with the core compositions, the desired properties (spin, feel, distance, durability, etc.) of the resulting golf balls. Preferably, the cover is relatively thin and comprises of a blend of hard and/or soft resinous materials to further enhance the spin rate and feel of the balls.
In this regard, the spin rate and feel of a golf ball are particularly important aspects to consider when selecting a golf ball for play. A golf ball with the capacity to obtain a high rate of spin allows a skilled golfer the opportunity to maximize control over the ball. This is particularly beneficial when hitting a shot on an approach to the green.
Golfers have traditionally judged the softness of a ball by the sound of the ball as it is hit with a club. Soft golf balls tend to have a low frequency sound when struck with a club. This sound is associated with a soft feel and thus is desirable to a skilled golfer. Consequently, another object of the invention is to provide a golf ball having an enhanced feel and a pleasing sound on impact with a golf club.
These and other objects and features of the invention will be apparent from the following summary and description of the invention and from the claims.
The present invention achieves all of the foregoing objectives and provides, in a first aspect, a golf ball comprising a soft, high resilience, solid core, comprising, in part, a combination of high molecular weight polybutadiene rubbers, and a soft outer cover disposed about the core. The core preferably is relatively large and durable, and the cover preferably includes a specific combination of hard and/or soft, yet durable, resinous materials. Preferably, the ball is a two-piece ball.
The core and the overall compression of the balls of the present invention are relatively soft. The core has a PGA(copyright) compression of 90 or less, preferably, less than 80 and most preferably less than 75, and the overall ball has a similar PGA(copyright) compression. The hardness of the cover is adjusted so that it is soft enough that the PGA(copyright) compression of the ball is the same or lower than the core compression. The core and/or the ball may also be treated, such as with gamma radiation, to additionally improve the finished properties of the ball, such as C.O.R., scuff and melt resistance.
The polybutadiene rubbers preferably used in the particular combination include a first polybutadiene rubber that is obtained utilizing a cobalt catalyst and which exhibits a Mooney viscosity in the range of from about 70 to about 83. The combination of polybutadiene rubbers also includes a second polybutadiene rubber that is obtained utilizing a neodymium series catalyst and which exhibits a Mooney viscosity of from about 30 to about 70. The second polybutadiene rubber may comprise a blend of one or more neodymium catalyst rubbers. Optionally, one or more heavy weight fillers can be included in the core composition to further enhance the spin rate characteristics.
The preferred cover compositions used in the golf ball of this aspect include combinations of hard and/or soft resinous materials, such as ionomeric resins. These ionomers are blended to produce a soft, yet durable, cover.
In an additional aspect, the present invention provides a golf ball comprising a core that includes a particular combination of first and second polybutadiene rubbers, in particular weight proportions, and a cover generally enclosing the core which is formed from a certain combination of ionomers. Specifically, the core includes from about 30% by weight of a first polybutadiene rubber obtained from a cobalt or cobalt-based catalyst, and about 30% to about 45% by weight of a second polybutadiene rubber obtained from a neodymium or lanthanide-series catalyst. The second polybutadiene rubber may comprise a blend of one or more neodymium and/or lanthanide-series catalyst rubbers.
The cover of the golf ball of this aspect includes a blend of a sodium ionomer and a zinc ionomer. The cover and overall ball can be irradiated (i.e., gamma treatment) to enhance various characteristics of the ball.
In yet another aspect, the present invention provides a golf ball comprising a core including a certain combination of polybutadiene rubbers, which is enclosed with a cover formed from a particular set of ionomers. The core includes from about 20% to about 30% by weight of a first polybutadiene rubber obtained from a cobalt catalyst and which exhibits a Mooney viscosity in the range of from about 70 to about 83. The core further includes from about 30% to about 45% of a second polybutadiene rubber obtained from a neodymium catalyst and which exhibits a Mooney viscosity of from about 30 to about 70. The second polybutadiene rubber may comprise a blend of one or more neodymium catalyst rubbers.
An ionomeric cover is then disposed about the core. This produces a relatively soft covered golf ball having a low PGA(copyright) compression and a high spin rate potential.
Further scope of the applicability of the invention will become apparent from the detailed description provided below.